1. Field of the Invention
This disclosure relates to electric-operated valves and fuel vapor treating systems each having such electric-operated valve.
2. Description of the Related Art
A gas vehicle is equipped with a fuel vapor treating system for preventing fuel vapor vaporized in a fuel tank from flowing into the atmosphere. The fuel vapor treating system includes an adsorbent canister filled with an adsorbent and temporarily trapping the fuel vapor by removably adsorbing the fuel vapor onto the adsorbent. The fuel vapor treating system has valves, each of which is generally composed of an electromagnetic valve, for opening and closing pipes communicating the fuel tank, the canister and the atmosphere each other in order to control flow of the fuel vapor in the fuel vapor treating system.
Japanese Laid-Open Patent Publication No. 2005-291241 discloses a conventional electromagnetic valve having a first valve member and a second valve member. FIG. 13 is a cross-sectional view showing a main part of the electromagnetic valve. FIG. 14 is a cross-sectional view showing the main part where the first valve member is open. FIG. 15 is a cross-sectional view showing the main part where the second valve member is open. As shown in FIG. 13, the electromagnetic valve 210 has the first valve member 250, the second valve member 270, a second valve seat 217 and an electromagnetic driving member (not shown), and defines a first passage 300 and a second passage 302 therein. The first valve member 250 is reciprocated in an axial direction (horizontal direction in FIG. 13). The second valve member 270 has a first valve seat 276 and defines a communication pathway 272 therein such that the communication pathway 272 communicates the first passage 300 and the second passage 302 with each other. When the first valve member 250 contacts the first valve seat 276 of the second valve member 270, the communication pathway 272 is closed. The second valve seat 270 is configured to fit the second valve seat 217. In addition, the second valve member 270 is biased in a valve-opening direction (leftward direction in FIG. 13) due to a spring 278.
When the first valve member 250 contacts the first valve seat 276 and the second valve member 270 contacts the second valve seat 217, communication between the first passage 300 and the second passage 302 is blocked (FIG. 13). When the electromagnetic driving member moves the first valve member 250 away from the first valve seat 276 while the second valve member 270 is contacting the second valve seat 217, the first passage 300 and the second passage 302 are communicated with each other via the communication pathway 272 (FIG. 14). Thus, fluid (fuel vapor) can flow from the first passage 300 through the communication pathway 272 to the second passage 302. In this state, when differential pressure between internal pressure of the first passage 300 and that of the second passage 302 decreases, the spring 278 moves the second valve member 270 away from the second valve seat 217 (FIG. 15). Accordingly, because an opening area (passage area) increases, i.e., the fluid can flow through a space between the second valve member 270 and the second valve seat 217 in addition to the communication pathway 272, it is able to increase a flow rate of the fluid flowing from the first passage 300 to the second passage 302.
As for this electromagnetic valve 210, in the condition that the first valve member 250 is kept away from the first valve seat 276 (FIG. 14), when a pressing force provided by the differential pressure between the internal pressure of the first passage 300 and the second passage 302 and acting on the second valve member 270 is greater than a spring force of the spring 278, the second valve member 270 is kept in contact with the second valve member 217. On the other hand, when the pressing force is lower than the spring force of the spring 278, the second valve member 270 is displaced away from the second valve seat 217 due to action of the spring.
In addition, in the condition that the first valve member 250 and the second valve member 270 contact the first valve seat 276 and the second valve seat 217, respectively (FIG. 13), when the internal pressure of the first passage 300 becomes higher or lower than the internal pressure of the second passage 302 by more than a predetermined value, it is not able to control the differential pressure between the internal pressures of the first passage 300 and the second passage 302 within a predetermined range. Therefore, it is necessary to define a bypass pathway for bypassing the electromagnetic valve 210 and to provide a relief valve in the bypass pathway in order to control the pressure difference between the internal pressures of the first passage 300 and the second passage 302 within the predetermined range. Thus, there has been need for improved valves.